A system is a set of interacting and/or interdependent components functioning as a whole. Over time, each of the various components in a given system may degrade at different relative rates. Moreover, as some components tend to serve a more critical role than others in the overall function of the system, the degradation of a given component can uniquely impact system performance relative to degradation of the other components in the same system. For instance, a gradual degradation of certain vehicle sensors may affect measurement accuracy without causing an appreciable degradation in overall vehicle performance, while a degraded battery may significantly reduce the vehicle's ability to start or function in certain operating modes.
Various onboard diagnostic approaches may be used to measure the performance of a particular component relative to calibrated thresholds. For instance, it is common to measure a battery output voltage and compare this value to calibrated high/low voltage thresholds. An operator may be made aware of the need to repair a given component when the component is no longer functioning properly with respect to such thresholds. System function typically improves when a severely degraded component is eventually repaired. However, immediate repair is not always a convenient or desirable option.